I have included the slideshow plugin on my image and album pages but it seems that the slideshow plugin will not show up if there is only 1 image in the album? The button doesn't print?

Any ideas?

Put more images in the album? Not much use for a slideshow if there is only one image.

The idea that the image goes full screen is the main concept for having it

Any little hack etc. to do this?

I agree that a slideshow with one image is pretty senseless :-) Why don't you just use the colorbox plugin?

Please enlighten me

How do I integrate such thing?

See the Zenpage theme image.php for an example.

Documentation of colorbox itself:
http://www.jacklmoore.com/colorbox/

I switched to that theme and all I get is this error:

Fatal error: Call to undefined function printHeadTitle() in /home/u538472778/public_html/newgallery/themes/zenpage/gallery.php on line 11

EDIT: Fixed this by re uploading the theme files!

Also, all I could find was this:

Which is what I had already?

Looked at the of the Zenpage theme's image.php? Do a file search on "colorbox" and review the documentation I linked. Colorbox works like bascially any other "lightbox" script. A bit you need to do yourself :-)